a) Field of the Invention
This invention relates to a drag strip suitable for use in a one-way clutch, and especially to a drag strip having at least two bent portions at such positions that when the drag strip is assembled in the one-way clutch, the two bent portions are kept out of contact with an inner circumferential surface of an inner retainer and an outer circumferential surface of an inner ring.
b) Description of the Related Art
A sprag-synchronized one-way clutch is constructed inter alia of an outer ring having an inner circumferential surface, an inner ring having an outer circumferential surface disposed in a mutually-opposing concentric relationship with the inner circumferential surface, plural sprags arranged in an annular space formed between these inner and outer circumferential surfaces, an outer and inner retainers for holding these sprags at predetermined positions, and a ribbon spring applying a force to keep the sprags contacted with the outer and inner rings.
To ensure transmission of motion of an inner or outer ring as a driver ring to the sprags upon a sudden acceleration or deceleration or high-speed rotation of the driver ring in such a one-way clutch, frictional force applying means such as drag strips are disposed between the driver ring and its adjacent retainer.
These drag strips are attached especially to an inner retainer of a one-way clutch and upon insertion of an inner ring as a driver ring, a central flat strip portion of each drag strip is flexed so that the central flat strip portion is maintained under a predetermined force in contact with the inner ring. A dragging torque is therefore transmitted in the order of the drag strips, the inner retainer and sprags, thereby making it possible to reduce wearing of the sprags and also ensure engagement of the one-way clutch.
One example of conventional drag strips is illustrated in FIG. 8. This conventional drag strip, which is designated generally at numeral 1, is formed of a strip-shaped material having a flat strip portion 2 at a middle portion thereof and clips 7 of a turned square U-shaped cross-sectional shape formed at opposite end portions via bent portions 3, as viewed in the direction of the length of the drag strip 1.
As is depicted in FIG. 9, this drag strip 1 is attached at opposite ends thereof to the inner retainer 4 by the clips 7 and the inner retainer 4 is also supported by intermediate hangers 6. Upon insertion of an inner ring 5 into the inner retainer 4, the strip portion 2 of the drag strip 1 is flexed along the contour of a peripheral edge of the inner ring 5 so that the strip portion 2 outwardly protrudes in the direction of a radius of the inner ring 5. As a consequence, the inner ring 5 and the drag strip 1 are maintained in contact with each other under a predetermined pressure. Numeral 8 indicates a sliding area of an inner circumferential surface of the strip portion 2, at which the strip portion 2 is maintained in sliding contact with an outer circumferential surface of the inner ring 5.
The contact pressure between the inner ring 5 and the drag strip 1 can be set at various values depending on the application of the one-way clutch. Described basically, this contact pressure depends on the amount of a flexion of the drag strip 1 when the inner ring 5 has been inserted. To obtain an amount of flexion large enough to provide a sufficient contact pressure, it has heretofore been the practice to make the strip portion 2 of the drag strip 1 longer.
When the strip portion 2 of the drag strip 1 is made longer, the rigidity of the drag strip 1 is lowered. This leads not only to difficulty in setting a desired dragging force but also to susceptibility to breakage of the drag strip 1 due to an increased bending moment. Furthermore, it is necessary to use a material excellent in mechanical properties such as rigidity and abrasion resistance as a material for the drag strip 1. Therefore the increased length of the strip portion 2 has also resulted in high manufacturing cost.
Further, the conventional drag strip has at each clip portion thereof a single bent portion 3 formed in conformity with the radius of curvature of the inner retainer 4 as shown in FIG. 9. Because of the construction that the single bent portion 3 is formed at each clip portion and each clip 7 is fitted in a corresponding window portion of the inner retainer, the amount of flexion of the drag strip 1 varies depending on a raceway diameter of the inner ring so that an adequate spring force is hardly available. To provide a larger spring force, it may be contemplated to make the position of each clip farther from the area of contact between the drag strip 1 and the inner ring 5. This however result in the drawback that the strip portion becomes longer as described above.
With a view toward overcoming the above-described drawback, another drag strip has been proposed. As shown FIG. 10, this drag strip which is designated at numeral 10 is provided on each side of a strip portion 12 with bent portions 13a,13b which are bent in opposite directions. This improvement has made it possible to increase the rigidity of the drag strip, to reduce the strip thickness of the drag strip and also to reduce the circumferential length of the drag strip, thereby bringing about the advantage that the material cost can be saved. Because of the short length between the bent portions, however, the drag strip 10 is accompanied by the inconvenience that its spring force is too high. This has resulted in an unduly high contact pressure at a sliding area 18, leading to the drawback that premature wearing is unavoidable.